Metal wood club with improved hitting face

ABSTRACT

A hitting face of a golf club head having improved flexural stiffness properties. In one embodiment, the hitting face is made from multiple materials. Each material has a different tensile modulus of elasticity, where the center of the hitting face has a much higher tensile modulus of elasticity than the surrounding portions of the hitting face. This creates a stiff center and a more easily deflected concentric portion. In another embodiment, the materials have different yield strengths, where the center of the hitting face has a very high yield strength compared to the surrounding portions of the hitting face. The hitting face may then plastically deform around its periphery, while the center retains its original shape.

CROSS-REFERENCE TO RELATED APPLICATIONS

The present application is a continuation of co-pending U.S. patentapplication Ser. No. 11/370,542, filed Mar. 8, 2006, now U.S. Pat. No.7,682,262, which is a continuation-in-part of U.S. patent app. no.10/911,341, filed Aug. 4, 2004, now U.S. Pat. No. 7,207,898, which is acontinuation-in-part of U.S. patent application Ser. No. 10/428,061,filed May 1, 2003, now U.S. Pat. No. 7,029,403, which is acontinuation-in-part of U.S. patent application Ser. No. 09/551,771,filed Apr. 18, 2000, now U.S. Pat. No. 6,605,007, the disclosures ofwhich are incorporated herein by reference in their entireties.

FIELD OF THE INVENTION

The present invention relates to an improved golf club head. Moreparticularly, the present invention relates to a golf club head with animproved striking face having a relatively large zone of high initialball velocity.

BACKGROUND

The complexities of golf club design are well known. The specificationsfor each component of the club (i.e., the club head, shaft, grip, andsubcomponents thereof) directly impact the performance of the club.Thus, by varying the design specifications, a golf club can be tailoredto have specific performance characteristics.

The design of club heads has long been studied. Among the more prominentconsiderations in club head design are loft, lie, face angle, horizontalface bulge, vertical face roll, center of gravity, inertia, materialselection, and overall head weight. While this basic set of criteria isgenerally the focus of golf club engineering, several other designaspects must also be addressed. The interior design of the club head maybe tailored to achieve particular characteristics, such as the inclusionof hosel or shaft attachment means, perimeter weights on the club head,and fillers within hollow club heads.

Golf club heads must also be strong to withstand the repeated impactsthat occur during collisions between the golf club and the golf ball.The loading that occurs during this transient event can create a peakforce of over 2,000 lbs. Thus, a major challenge is designing the clubface and body to resist permanent deformation or failure by materialyield or fracture. Conventional hollow metal wood drivers made fromtitanium typically have a uniform face thickness exceeding 2.5 mm toensure structural integrity of the club head.

Players generally seek a metal wood driver and golf ball combinationthat delivers maximum distance and landing accuracy. The distance a balltravels after impact is dictated by the magnitude and direction of theball's translational velocity and the ball's rotational velocity orspin. Environmental conditions, including atmospheric pressure,humidity, temperature, and wind speed, further influence the ball'sflight. However, these environmental effects are beyond the control ofthe golf equipment manufacturer. Golf ball landing accuracy is driven bya number of factors as well. Some of these factors are attributed toclub head design, such as center of gravity and club face flexibility.

The United States Golf Association (USGA), the governing body for therules of golf in the United States, has specifications for theperformance of golf balls. These performance specifications dictate thesize and weight of a conforming golfball. One USGA rule limits the golfball's initial velocity after a prescribed impact to 250 feet persecond±2% (or 255 feet per second maximum initial velocity). To achievegreater golf ball travel distance, ball velocity after impact and thecoefficient of restitution of the ball-club impact must be maximizedwhile remaining within this rule.

Generally, golf ball travel distance is a function of the total kineticenergy imparted to the ball during impact with the club head, neglectingenvironmental effects. During impact, kinetic energy is transferred fromthe club and stored as elastic strain energy in the club head and asviscoelastic strain energy in the ball. After impact, the stored energyin the ball and in the club is transformed back into kinetic energy inthe form of translational and rotational velocity of the ball, as wellas the club. Since the collision is not perfectly elastic, a portion ofenergy is dissipated in club head vibration and in viscoelasticrelaxation of the ball. Viscoelastic relaxation is a material propertyof the polymeric materials used in all manufactured golf balls.

Viscoelastic relaxation of the ball is a parasitic energy source, whichis dependent upon the rate of deformation. To minimize this effect, therate of deformation must be reduced. This may be accomplished byallowing more club face deformation during impact. Since metallicdeformation may be purely elastic, the strain energy stored in the clubface is returned to the ball after impact thereby increasing the ball'soutbound velocity after impact.

A variety of techniques may be utilized to vary the deformation of theclub face, including uniform face thinning, thinned faces with ribbedstiffeners and varying thickness, among others. These designs shouldhave sufficient structural integrity to withstand repeated impactswithout permanently deforming the club face. In general, conventionalclub heads also exhibit wide variations in initial ball speed afterimpact, depending on the impact location on the face of the club. Hence,there remains a need in the art for a club head that has a larger “sweetzone” or zone of substantially uniform high initial ball speed.

SUMMARY OF INVENTION

According to the invention, a golf club head includes a hitting facehaving a central zone made of a first material, wherein the central zonehas a first tensile modulus of elasticity. A second zone, concentricwith the central zone, is made of a second material having a secondtensile modulus of elasticity. The first tensile modulus of elasticityis higher than the second tensile modulus of elasticity.

BRIEF DESCRIPTION OF THE DRAWINGS

Preferred features of the present invention are disclosed in theaccompanying drawings, wherein similar reference characters denotesimilar elements throughout the several views, and wherein:

FIG. 1 is a front, exploded view of a golf club head according to thepresent invention as disclosed in the parent application;

FIG. 2 is a perspective view of a golf club head according to thepresent invention as disclosed in the parent application;

FIG. 3 is an inverted perspective view of the golf club head of FIG. 2;

FIG. 4 is a perspective view of an alternate embodiment of a golf clubhead according to the present invention;

FIG. 5 is a top view of the golf club head of FIG. 4;

FIG. 6 is an exploded perspective view of the golf club head of FIG. 4;

FIG. 7 is a perspective view of the hitting face of the golf club headof FIG. 4; and

FIG. 8 is an exploded view of the hitting face of FIG. 7.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT

Priority U.S. Pat. No. 6,605,007, which has been incorporated herein inits entirety, discloses an improved golf club that also produces arelatively large “sweet zone” or zone of substantially uniform highinitial velocity or high coefficient of restitution (COR).

COR or coefficient of restitution is a measure of collision efficiency.COR is the ratio of the velocity of separation to the velocity ofapproach. In this model, therefore, COR was to determined using thefollowing formula:

(v_(club-post)−v_(ball-post))/(v_(ball-pre)−v_(club-pre))

where,

-   -   v_(club-post) represents the velocity of the club after impact;    -   v_(ball-post) represents the velocity of the ball after impact;    -   v_(club-pre) represents the velocity of the club before impact        (a value of zero for USGA CUR conditions); and    -   v_(ball-pre) represents the velocity of the ball before impact.

COR, in general, depends on the shape and material properties of thecolliding bodies. A perfectly elastic impact has a CUR of one (1.0),indicating that no energy is lost, while a perfectly inelastic orperfectly plastic impact has a COR of zero (0.0), indicating that thecolliding bodies did not separate after impact resulting in a maximumloss of energy. Consequently, high COR values are indicative of greaterball velocity and distance.

As shown in FIG. 1, which corresponds to FIG. 2 of the parent 141application, the accuracy of the club and the club's large zone ofuniform high initial velocity are produced by hitting face 2, havingcentral zone 4, and a surrounding intermediate zone 6, and an optionaltransition zone 7 between central zone 4 and intermediate zone 6.Preferably, the area of central zone 4 comprises about 15% to about 60%of the total area of the hitting face 2, and more preferably about 20%to about 50%.

Central zone 4 is comparatively rigid and intermediate zone 6 isrelatively flexible so that upon ball impact, intermediate zone 6 offace 2 deforms to provide high ball velocity, while central zone 4 issubstantially undeformed so that the ball flies on-target. Thus, uponball impact the deformation of intermediate zone 6 allows central zone 4to move into and out of a club head 10 as a unit. Surroundingintermediate zone 6 may alternatively be located directly adjacent tocentral zone 4. As a result, the head exhibits a coefficient ofrestitution greater than about 0.81.

The above is accomplished by providing central zone 4 with a firstflexural stiffness and intermediate zone 6 with a second flexuralstiffness. Flexural stiffness (FS) is defined as each portion's averageelastic modulus (E) times each portion's average thickness (t) cubed or

FS=Et³  Eq. 1

The calculation of averages of modulus and thickness is hilly disclosedin the parent applications and in the '007 patent, which have previouslybeen incorporated by reference in their entireties. The determination ofES when the thickness varies or when the material is anisotropic is alsofully discussed in the parent patent applications and in the '007patent.

Since the flexural stiffness is a function of material and thickness,the following techniques can be used to achieve the substantialdifference between the flexural stiffness of central zone 4 andintermediate zone 6: 1) different materials can be used for eachportion, 2) different thicknesses can be used for each portion, or 3)different materials and thickness can be used for each portion. Forexample, in a preferred embodiment, the thickness of the central zone isgreater than the thickness of the intermediate zone and the material forboth portions is the same.

In club head 10, the above flexural stiffness relationships can beachieved by selecting a certain material with a particular elasticmodulus and varying the thickness of the zones. In another embodiment,the flexural stiffness relationships can be achieved by varying thematerials of the zones with respect to one another so that the zoneshave different elastic moduli and the thickness is changed accordingly.Thus, the thickness of the zones can be the same or different dependingon the elastic modulus of the material of each zone. It is also possibleto obtain the required flexural stiffness ratio through the use ofstructural ribs, reinforcing plates, and thickness parameters. Theparent applications and the '007 patent describe in detail many of thesealternative structures as well as the preferred ranges of ratios offlexural stiffness between central zone 4 and intermediate zone 6.

Further, as discussed in the '007 patent, two or more differenthomogeneous materials may be used to form hitting face 2. For example,central zone 4 may be of generally uniform thickness and made from astainless steel having a Young's Modulus of 30.0×10⁶ lbs/in². Theadjacent intermediate zone 6 has a continuously tapering thickness fromthe pace perimeter toward central zone 4. The thickness of intermediatezone 6 is defined to change linearly. Intermediate zone 6 is made from atitanium alloy having a Young's Modulus of 16.5×10⁶ lbs/in².

Referring now to FIGS. 2-3, another embodiment from the parent '341application is shown. In this embodiment, central zone 4 of hitting face2 is formed with a face insert 42. Face insert 42 is preferably weldedto club head 10 along weld line 20. Face insert 42 includes a polygonalor elliptical main plate 34 and a sidewall or wing 70 that extends intoand forms a part of crown 14. As such, an upper portion 71 of weld line20 is removed to crown 14. As the stress line created by weld line 20 isremoved from hitting face 2, the probability of failure along upperportion 21 due to repeated impact with golf balls is reduced.

Face insert 42 is preferably made from the same material as the rest ofclub head 10, such as titanium, a titanium alloy, steel, or any othermaterial suitable for use as a club head. Face insert 42 is preferablythe same thickness as the rest of club head 10, although face insert 42may be made thicker or thinner in order to affect the flexural stiffnessthereof.

The size and shape of face insert 42 may vary. As stated above,preferably, face insert 42 is a modified oval U-cup or L-cup, but it mayalso be other shapes, such as rectangular, elliptical or circular. Faceinsert 42 preferably forms nearly the entire surface area of hittingface 2. However, face insert 42 may form a much smaller portion ofhitting face. Also, wing 70 may extend into and form a part of sole 22,as shown in FIG. 3, by simply inverting the configuration of face insert42. In this case, the affected weld line is lower weld line 73.

The material properties of face insert 42 can also be affected by themethod chosen to form face insert 42. For example, face insert 42 ispreferably stamped from sheet metal after the metal has been cold rolledor cold worked in order to align the crystal grains of the metal.Stamping metal in this fashion produces a stronger hitting face thanother manufacturing techniques. Further, face insert 42 is thenpositioned within hitting face 2 so that the grain flow pattern of faceinsert 42 runs in a sole-to-crown direction. Alternatively, the grainflow pattern of face insert 42 may run in a heel-to-toe direction or ina diagonal direction. Other methods known in the art may also be used tomanufacture face insert 42, such as forging and casting.

Preferably, face insert 42 is made by milling or stamping and forming.In the manufacturing process, a malleable metal suitable for use as ahitting face, such as titanium, titanium alloy, carbon steel, stainlesssteel, beryllium copper, and other forgeable metals, is heated and thenhammered into the desired shape of the face cup. Examples of someappropriate metals include but are not limited to titanium 6-4 alloy,titanium 15-3-3-3 alloy, titanium 20-4-1 alloy, and DAT 55 and DAT 55G,titanium alloys available from Diado Steel of Tokyo, Japan.

The preferred forging process is die or billet forging, in which apre-measured rod of forgeable metal is heated and placed between a die,which contains the desired shape of face insert 42, and a hammer. Theheated metal is then hammered into the desired shape. An advantage offorging face insert 42 is that the thickness of the face can be as thinas about 0.060 inch (or about 1.5 mm) around the perimeter or edgethereof.

Referring now to FIGS. 4-8, yet another embodiment of the presentinvention is shown. This embodiment combines features from both of thepreviously discussed embodiments, namely having a hitting face insert 42with and a central zone insert 44 disposed in a main plate portion 34.As can be seen most clearly in FIGS. 7-8, central zone insert 44 is agenerally flat piece having any shape known in the art, such aspolygonal, oval, or, as shown, an irregular shape. Main plate portion 34serves as a support to which central zone insert 44 is attached, such asby welding.

As is known in the art, a weld line or joint is an area ofdiscontinuity, where even if two pieces of the same material are joined,the structural properties of the pieces in the vicinity of the joint arealtered. Removing weld lines to the crown or the sole of a club headallows the thickness of the hitting face to be controlled more preciselyand allows for a thinner overall hitting face. The joints can also beused to alter the properties of the hitting face. In accordance withthis aspect of the invention, hitting face insert 42 preferably includesoptional extension portions 70, 73 which may form part of crown 14and/or part of sole 22.

Preferably, two different materials are chosen to make up hitting faceinsert 42. The first material is used to form central zone insert 44,and the second material is used to form the remainder of hitting faceinsert 42. In other words, the central zone 4 of this embodiment,similar to the central zones described above, is made of the firstmaterial, and the transition zone 7 of this embodiment, also similar tothe transition zones described above, is made of the second material.The intermediate zone 6 of this embodiment is formed on a face support30 of hitting face 2 forms, similar to the intermediate zones describedabove. In this embodiment, intermediate zone 6 may be made of either thefirst material, the second material, or a completely different material.Also, a portion of intermediate zone 6 may be located on hitting faceinsert 42. Central zone insert 44 may have either uniform or varyingthickness, and its thickness may be the same as or different from thatof hitting face insert 42.

The first alloy is chosen such that its tensile modulus of elasticity,ε₁, is significantly greater than the tensile modulus of elasticity ofthe second alloy, ε₂. Preferably, the ratio of ε₁ to ε₂, is a high asmaterially practicable. Examples of appropriate materials includetitanium alloys. Preferably, the materials chosen are capable of beingwelded to each other.

The performance of hitting face 2 of golf club head 10, especially thosethat are designed to be drivers, are generally equated to the physics ofplate behavior. Typical characteristics that can be expressed in aformula to assess the behavior of the plate with regard to deflectionsand stresses take the form of a constant known in the art fromfundamental plate theory using standard assumptions to produce thefollowing simplified equation:

D=εt ³/(12(1−ν²))  Eq. 2

where ε is the tensile modulus of elasticity, t is the thickness of theplate, and ν is Poisson's ratio. In a preferred embodiment, wheretitanium alloys are used, a ranges from about 700 Pa to about 128 GPa,and ν ranges from about 0.33 to about 0.35. The thickness of the plate tin the present invention will vary depending upon, inter alia,manufacturing techniques and the characteristics of the material, so theclub face can withstand the high and repeated impact forces from thecollision with golf balls over the life of the club.

The structural behavior of the hitting face may be controlled in part bychoosing alloys with different tensile moduli of elasticity. As is knownin the art, the solution for the deflection w of a circular plate havingradius a and loaded at its center with a point load P, is as follows:

w=Pa ²/(16πD)  Eq. 3

Thus, the deflection w is determined, in part, by the tensile modulus ofelasticity a of the material of the circular plate. While hitting faceinsert 42 nor central zone insert 44 is a perfect circular plate, thedeflection of both hitting face insert 42 and central zone insert 44 maybe approximated using Eq. 3. As is known in the art, the actualdeflection w of a plate having specific material properties andthickness may be determined using a variety of techniques, includingFinite Element Analysis.

Alternatively, the first and second materials have different elongationand yield strengths. Preferably, central zone insert 44 is made of afirst material with a very high yield strength, while main plate 34 andextension portions 70, 73 of hitting face insert 42 are made of a secondmaterial with a significantly lower yield strength. For the purposes ofexample only, central zone insert 44 may be made from titanium whilemain plate 34 and extension portions 70, 73 may be made from steel. Byusing a lower yield strength material, this embodiment can takeadvantage of the lower yield strength material's plastic deformationbehavior. When impacted by a golf ball, hitting face 2 is subjected tostress due to the force of impact. Once a portion of hitting face 42 hasseen a stress level beyond its yield strength, that portion elongates.As central zone insert 44 has a very high yield strength compared to thesurrounding portion of hitting face 42, main plate 34 will slightlyplastically deform while central zone insert 44 experiences no suchplastic deformation. In essence, the periphery of main plate 34 willbehave like a hinge for central zone insert 44 so that the impact stresswill be redistributed to the stiffer areas of hitting face 42.

While various descriptions of the present invention are described above,it should be understood that the various features of each embodimentcould be used alone or in any combination thereof. Therefore, thisinvention is not to be limited to only the specifically preferredembodiments depicted herein. Further, it should be understood thatvariations and modifications within the spirit and scope of theinvention might occur to those skilled in the art to which the inventionpertains. For example, the face and/or individual zones can havethickness variations in a step-wise or continuous fashion. Othermodifications include a perimeter zone that has a thickness that isgreater than or less than the adjacent, intermediate zone. In addition,the shapes of the central, intermediate, and perimeter zones are notlimited to those disclosed herein. Accordingly, all expedientmodifications readily attainable by one versed in the art from thedisclosure set forth herein that are within the scope and spirit of thepresent invention are to be included as further embodiments of thepresent invention. The scope of the present invention is accordinglydefined as set forth in the appended claims.

1. A golf club head comprising: a hitting face having a face insertcoupled around a perimeter thereof to the golf club head, the hittingface comprising a central zone insert comprising a first material, and asecond zone, wherein the second zone is concentric with the central zoneinsert and attached to the central zone insert around a perimeterthereof, wherein the second zone comprises a second material differentthan the first material, and wherein the second material has a loweryield strength than the first material and the dimensions of the centralzone insert and the second zone are selected such that the second zoneplastically deforms while the central zone insert elastically deformsdue to the impact force of striking a golf ball.
 2. The golf club headof claim 1, wherein the central zone is homogeneous.
 3. The golf clubhead of claim 2, wherein the second zone is homogeneous.
 4. The golfclub head of claim 1, wherein the hitting face further comprises anintermediate zone surrounding the central zone insert.
 5. The golf clubhead of claim 4, wherein the intermediate zone is constructed from thefirst material.
 6. The golf club head of claim 4, wherein theintermediate zone is constructed from the second material.
 7. The golfclub head of claim 4, wherein the intermediate zone is constructed froma third material that is different than the first material and thesecond material.
 8. The golf club head of claim 1, wherein the centralzone insert provides a central zone area that is between about 15% andabout 60% of a total face area.
 9. The golf club head of claim 8,wherein the central zone insert provides a central zone area that isbetween about 20% and about 50% of the total face area.
 10. The golfclub head of claim 1, wherein the face insert is welded to the clubhead.
 11. The golf club head of claim 1, wherein the central zone insertis welded to the second zone.
 12. The golf club head of claim 1, whereinthe face insert further comprises a crown extension.
 13. The golf clubhead of claim 1, wherein the face insert further comprises a soleextension.
 14. The golf club head of claim 1, wherein the first andsecond materials comprise alloys of the same material.
 15. The golf clubhead of claim 13, wherein the same material is titanium.